Shock-Tube Study of the Vibrational Relaxation of Nitric Oxide

Abstract

The vibrational relaxation time of nitric oxide in NO–Ar mixtures was determined over the temperature range 1500°—7000°K. An ultraviolet absorption technique using 1270-A radiation was employed to monitor the vibrational temperature as a function of time after these mixtures were shock heated to high translational temperatures. P10, the transition probability per oscillator per collision for transition between vibrational levels 1 and 0 calculated from the measured relaxation times ranged from 1.0×10—3 at 1500°K to 2.8×10—2 at 7000°K for NO–NO collisions. Argon is about 1/50 as efficient as NO. The results are compared with the lower temperature (400°—1500°K) work of Robben and with the adiabatic theory of Schwartz, Slawsky, and Herzfeld and the nonadiabatic theory of Nikitin.